The present invention relates to a method for joining studs to workpieces, in particular for the purpose of stud welding, and to a joining appliance for executing such a method.
Various methods for joining fastening elements, such as studs, to a workpiece, such as a plate, are known in the prior art. There is known, for example, the practice of adhesive-bonding or thermoplastically welding fastening elements to component parts. Further, so-called stud welding is an established process for welding metallic fastening elements to metallic workpieces.
These types of joining method are used extensively in the automobile industry, for example, wherein studs are joined to workpieces such as vehicle-body plates or other vehicle-body portions. The studs then frequently serve as anchors for fastening mount-on parts or for clipping-on plastic clips to which, in turn, other component parts can be fixed, such as electrical lines, brake hoses, etc.
In industrial application, these types of joining method are usually automated, a joining head usually being guided in an automated manner by a robot. Further, there is known the practice of automated feeding of the studs to the joining head, for example by means of compressed air. In the joining head, the studs are then usually each held singly by a holding device or a gripper, before they are joined to the workpiece.
Known in this case is the practice of acquiring a dimension of a stud to be joined, before the actual joining operation, through application of a sensing element to the stud and through acquisition of a travel distance of the sensing element required for this purpose. It can thereby be ensured, for example, that studs of the correct shank diameter are joined. In the case of the sequential processing of studs of differing dimensions, in particular, such a measuring operation before the actual joining operation is of particular importance. In the event of an incorrect stud being erroneously present in the joining head, it can still be removed before the actual joining operation is performed. Elaborate repair works can thereby be avoided. In this case, the dimension of the stud is generally compared with an allowable tolerance range.